Table 4.

Subgroup analysis - the effect on primary outcomes

	No. of studies	Helmet NIV event/total	Control event/total	I2 (%)	P value for heterogeneity	OR 95 % CI	Overall effect Z/P value
Hospital mortality
Type of ARF
Hypercapnic	2	8/58	11/56	0	0.8	0.65 [0.28, 2.06]	0.81/0.42
Hypoxemic	5	29/153	62/182	0	0.97	0.38 [0.22, 0.65]	3.49/0.0005
Ventilation mode in the experimental group
CPAP	2	6/57	15/58	0	0.79	0.30 [0.10, 0.89]	2.17/0.03
PSV	5	31/154	58/180	0	0.77	0.46 [0.27, 0.79]	2.8/0.005
Interfaces used in the control group
Facial mask	6	35/171	66/197	0	0.97	0.45 [0.27, 0.74]	3.12/0.002
Venturi mask	1	2/40	7/41	NA	NA	0.26 [0.05, 1.32]	1.63/0.1
Intubation rate
Type of ARF
Hypercapnic	5	15/132	29/132	0	0.42	0.42 [0.20, 0.85]	2.41/0.02
Hypoxemic	5	33/153	88/143	61	0.03	0.28 [0.17, 0.45]	5.16/<0.0001
Ventilation mode in the experimental group
CPAP	2	10/57	34/58	42	0.19	0.16 [0.07, 0.36]	4.28/<0.0001
PSV	8	38/228	83/256	30	0.19	0.39 [0.25, 0.62]	4.05/<0.0001
Interfaces used in the control group
Facial mask	8	42/206	89/232	29	0.2	0.39 [0.25, 0.61]	4.16/<0.0001
Oronasal mask	1	0/39	2/41	NA	NA	0.20 [0.01, 4.30]	1.03/0.3
Venturi mask	1	6/40	26/41	NA	NA	0.32 [0.21, 0.47]	5.56/<0.0001
Complications
Type of ARF
Hypercapnic	3	20/97	35/97	77	0.01	0.45 [0.23, 0.86]	2.42/0.02
Hypoxemic	6	28/164	48/193	17	0.30	0.76 [0.43, 1.32]	0.98/0.33
Ventilation mode in the experimental group
CPAP	3	7/68	7/69	57	0.10	1.01 [0.36, 2.89]	0.03/0.98
PSV	6	41/193	76/221	46	0.10	0.55 [0.34, 0.87]	2.35/0.06
Interfaces used in the control group
Facial mask	7	31/182	72/208	25	0.24	0.40 [0.24, 0.67]	3.49/0.0005
Oronasal mask	1	11/39	9/41	NA	NA	1.40 [0.51, 3.86]	0.64/0. 52
Venturi mask	1	6/40	2/41	NA	NA	3.44 [0.65, 18.2]	1.45/0.15

NIV noninvasive ventilation, OR odds ratio, CI confidence interval, ARF acute respiratory failure, CPAP continuous positive airway pressure, PSV pressure support ventilation, NA not applicable